KR100302361B1 - Aldehyde-modified cellulosic fibers for paper products having high initial wet strength - Google Patents

Abstract

Modified cellulose fibers are prepared by (1) esterifying cellulose fibers with 1,2-disubstituted alkenes having one or more carboxylic acid groups reactive with cellulose hydroxyl groups, and (2) oxidizing the esterified fibers to form aldehyde groups. Modified fibers are useful in paper products that tend to have temporary wet strength. Strength additives may be included in paper products to impart high temporary wet strength or high permanent wet strength.

Description

ALDEHYDE-MODIFIED CELLULOSIC FIBERS FOR PAPER PRODUCTS HAVING HIGH INITIAL WET STRENGTH}

Wet strength is a desirable property of many disposable paper products that come into contact with water during use, such as napkins, paper towels, kitchen tissues, disposable hospital clothing, and the like. In particular, it is often desirable for such paper products to have sufficient wet strength for use under wet or wet conditions. Thus, a product must have its original shape substantially during anti-tear, anti-ripping, anti-collapse, etc. during its intended use. For example, wet tissues or towels may be used to clean the body or the like. Unfortunately, untreated assemblies of unmodified cellulose fibers typically lose between 95% and 97% of their strength when saturated with water, and generally cannot be used under wet or wet conditions.

As is known in the art, paper products cause dry strength in part by hydrogen bonding between the fibers. If the paper product is wet, water interferes with hydrogen bonding and consequently reduces the strength of the paper product. Historically, two approaches have primarily increased the wet strength of paper products. One approach is to inhibit water from reaching the hydrogen bonds and interfering with the hydrogen bonds, for example by coating the paper product. Another approach is to mix additives that form intermolecular bonds that are not cleaved by water for wet strength or that contribute to transient wet strength that is not cleaved by water. The second approach is a technique of general choice, in particular for tissue products. In the latter approach, water soluble wet strength resins may generally be added to the pulp before the paper product is formed (wet-end addition). Resins generally contain cation functionality and can easily contain cellulose fibers that are naturally anionic.

Many resins have been used or disclosed as being particularly useful for providing wet strength in paper products. Some of these wet strength additives form paper products having permanent wet strength, i.e., paper that retains a substantial portion of its initial wet strength over time when placed in a receiving medium. Examples of this type of resin include urea formaldehyde resins, melamine-formaldehyde resins and polyamide-epichlorohydrin resins. Such resins limit the decay of wet strength.

Thus, recently manufacturers have added temporary wet strength additives to paper products for paper products where the wet strength declines when submerged while providing sufficient wet strength for the intended use. Decreasing wet strength facilitates the flow of paper products in sewage systems. Many approaches have been proposed to provide paper products claimed to have good initial wet strength that rapidly decays over time. For example, US Pat. No. 3,096,228 to Day et al., July 2, 1983; US Pat. No. 3,556,932 to Coscia et al., January 19, 1971; 6, 1973 U.S. Patent No. 3,740,391 to Williams et al. On May 19, U.S. Patent No. 4,605,702 to Guerro et al. On August 12, 1986, and Solarek on June 23, 1987. US Pat. No. 4,675,394 to Solarek et al. Proposes a number of approaches for obtaining temporary wet strength with polymers or other compounds.

See, eg, T.G.Gafurov et al., Strukt. Modif. Khlop. Tsellyul., Vol. 3, pp. 131-135 (1966), it is also known to modify cellulose fibers to contain aldehyde groups.

Although the art provides a paper product having an initial wet strength, neither method provides a paper product by the method of the present invention. It is now known that paper products containing modified fibers produced by reacting cellulose fibers with 1,2-disubstituted carboxyl alkenes and then oxidizing are given wet strength.

It is an object of the present invention to provide cellulose fibers modified to contain aldehyde groups and paper tissue products such as toilet paper containing such fibers. In addition, it is an object of the present invention to provide a paper product having wet strength. Another object of the present invention is to provide a paper product having a temporary wet strength.

Summary of the Invention

FIELD OF THE INVENTION The present invention relates to cellulose fibers modified to contain aldehyde groups. The invention also relates to paper products containing such fibers. Modified fibers tend to provide paper products with a high temporary initial wet tensile strength (eg, at least about 80 g / inch, preferably at least about 12 g / inch).

Preferred modified cellulose fibers of the present invention are formed by reacting a carboxyl group of 1,2-disubstituted carboxyl alkenes with a portion of the hydroxy group of the cellulose fiber to oxidize covalently bonded cellulose fibers. Preferably the alkenes preferably have one or more carboxyl groups so that the alkene can form anhydrides.

The present invention relates to modified cellulose fibers, more specifically modified cellulose fibers useful for providing paper products with good initial wet strength.

Modified cellulose fibers of the present invention may be formed by oxidizing covalently bonded cellulose fibers by reaction with 1,2-disubstituted alkenes containing one or more carboxyl functional groups capable of reacting with hydroxy groups of cellulose (1 , 2-disubstituted alkenes are optionally referred to herein as "carboxyl alkenes"). Cellulose fibers reacted with carboxyl alkenes prior to oxidation are herein referred to herein as "intermediate cellulose fibers" or "intermediate cellulose fiber reaction products".

Intermediate cellulose fibers can be derived from a number of cellulose fibers. Cellulose fibers of various natural sources can be used in the present invention. Decomposed fibers from softwood (derived from saline), decomposed fibers from hardwood (derived from deciduous) or decomposed fibers from cotton linters are preferably used. Fiber and cellulose fiber sources from Esparto grass, sugar cane, grandmother, flax and other woods may also be used as raw materials in the present invention. Cellulose fibers that are optimal for use in the present invention will depend on the intended specific intended use. Generally wood pulp will be used. Wood pulp that can be used includes chemical pulp (Kraft (i.e. sulfate) and sulfite pulp) and mechanical pulp (e.g. crushed wood pulp, thermomechanical pulp (i.e. TMP)) and chemical thermomechanical pulp (i.e. CTMP). Can be mentioned. However, chemical pulp is preferred because it imparts excellent softness to the tissue sheet produced. Fully bleached, partially bleached or unbleached fibers may also be used. It may often be desirable to use bleached pulp to provide good gloss and to appeal to consumers. For products such as tissue paper, absorbent pads for paper towels and diapers, sanitary napkins, sanitary ware and other similar absorbent paper products, it is preferable to use northern soft pulp because of the highest strength properties of northern soft pulp.

Recycled paper, which may contain any or all of the aforementioned categories of fibers and other non-fibrous materials such as fillers and adhesives, is also useful in the present invention.

Cellulose fibers react with 1,2-disubstituted alkenes containing one or more carboxyl functional groups to form intermediate fibers. The carboxyl functional group can be for example a carboxylic acid group (-COOH) or an acid amide group (-CONH ₂ ), preferably a carboxylic acid group. Carboxylic acid groups react with cellulose hydroxy groups to form ester linkages, as are acid amide groups. Acid amide groups, however, are somewhat less reactive than carboxylic acids and are therefore less preferred.

The term " 1,2-disubstituted " means that the double-bonded carbon has a single bond with each other carbon atom and hydrogen atom other than the double-bonded carbon atom (in the case of single bond with hydrogen atom, -HC = CH- Mean). While not wishing to be bound by theory, it is believed that formaldehyde is likely to form undesirably during the oxidation of intermediate cellulose fibers when the double bonded carbon atoms are each unbound with at least one carbon atom. On the other hand, when one or more carbon atoms are each bonded to a double bonded carbon atom, ketones are formed while the intermediate cellulose fiber is oxidized. Carboxylic alkenes may contain one or more carbon-carbon double bonds and may contain other multiple bonds.

The 1,2-disubstituted carbon-carbon double bond is preferably a cyclic structure. Cyclic alkenes tend to have less aldehyde loss during the oxidation process of intermediate cellulose fibers than acyclic alkenes. While not wishing to be bound by theory, the number of aldehyde groups is required in order to maximize the number of hemi-acetal groups and / or N-acyl hemiamino groups in the final paper product, thus maximizing the wet strength of paper products containing modified cellulose fibers. Should be maximized.

In a preferred embodiment, the carboxyl alkenes are polycarboxyl based compounds which can contain one or more carboxyl functional groups to form aldehydes. Such polycarboxyl-based compounds readily react with the hydroxyl groups of the cellulose fibers to form intermediate cellulose fibers, wherein the yield of the modified cellulose fibers of the invention is higher than when the carboxyl alkenes cannot form anhydrides. As used herein, the term “anhydride” refers to a chemical compound derived from an acid by removing water molecules from the acid. The second carboxyl functional group may suitably be a carboxylic acid group or an acid amide group. Thus, carboxyl alkenes may form dicarboxylic anhydrides or cyclic imides. It is preferable that a carboxylic acid group is a carboxylic acid group, respectively.

More preferably, the carbon atoms of the carboxyl groups of the polycarboxyl-based compound are separated into two to three carbon atoms to facilitate the formation of anhydrides (i.e., the positions of the carboxyl groups are 1,2 or 1,3 relative to each other). Location). Most preferably, the carbon atoms of the carboxyl group are separated by two carbon atoms since the 1,2 polycarboxyl-based compounds form anhydrides more easily than the 1,3 polycarboxyl-based compounds at lower temperatures.

The 1,2-disubstituted alkene and carboxyl functional groups are preferably unconjugated. Without wishing to be bound by theory, Michael Addition (1,4) can occur at the alkene bonds via esterification when the alkene and carboxyl groups are conjugated. This addition reaction breaks the alkene bonds and prevents the formation of aldehydes during the oxidation of the intermediate cellulose fibers.

Preferred carboxyl alkenes are water soluble and can be used in water-based methods. As used herein, the term "water soluble" refers to the ability of a substance to dissolve, disperse, swell, hydrate, or similarly mix in water. Means. Similarly, as used herein, phrases such as "substantially soluble", "substantially soluble", and the like, refer to the dissolution, dispersion, swelling, hydration, and mixing of materials in a liquid medium (eg, water). Refers to. The mixture typically forms a homogeneous fluid mixture, i.e. a physical single phase, in general.

Suitable carboxyl alkenes include, but are not limited to, cis-1,2,3,6-tetrahydrophthalic acid and 1,2,3,6-tetrahydrophthalic acid. Derivatives of such compounds are also useful herein, such as those in which carbon atoms other than double bonded carbon atoms are mono- or poly-substituted. Multiple substituents may be present. However, the substituents should not provide steric hindrance to reduce the rate of esterification or electronically deactivate the esterification step. Cis-1,2,3,6-tetrahydrophthalic acid is preferred as the carboxyl alkene because of its usefulness and fast reaction time.

The intermediate cellulose fibers may comprise the steps of preparing a fluid mixture of carboxyl alkenes and liquid medium; Contacting cellulose fibers with the liquid mixture to form treated fibers and reacting at least a portion of the hydroxy groups of the cellulose fibers with the carboxyl-based functional groups of the alkene to form covalent bonds. The resulting intermediate cellulose fiber is then oxidized to form aldehyde groups as described below.

Suitable liquid media are media capable of substantially dissolving or dispersing the carboxyl alkenes, preferably providing the maximum solubility of the carboxyl alkenes in the liquid mixture. The liquid medium may comprise one or more solvents for the carboxyl alkene compound. Suitable liquid media include water, pyridine, other protic solvents, and mixtures thereof. Water is the preferred liquid medium.

The carboxyl alkenes and liquid medium may be mixed or mixed together by any suitable method as is known in the art of forming solutions or dispersions. It is typically desirable to maximize the concentration of carboxyl alkenes in the fluid mixture to provide the modified cellulose fibers of the present invention in order to reduce the time and energy required to evaporate the liquid medium. Heating is necessary to improve the solubility of the carboxyl alkenes in the liquid medium. For example, the fluid mixture may be heated to a temperature of about 50 ° C to about 100 ° C.

Cellulose fibers can be contacted with a fluid mixture containing carboxyl alkenes by a combination of one or more techniques as known in the art of paper, such as immersion, mixing, dumping, spraying, dipping and pressing, and the like.

In a preferred embodiment, the cellulose fibers are contacted with the fluid mixture at the wet end of the paper machine during the pulp processing (ie, wet lamination paper making process) to produce the paper sheet. According to this embodiment, the pulp sheet is sprayed with the fluid mixture at the wet end of the process. For conventional commercial processes, the consistency of the sheet is greater than about 20%, preferably 20-50%, in order to maintain adequate wet strength. Surprisingly, it was found that the dry tensile strength and total initial wet strength of the paper sheet of the present invention increased with increasing basis weight of the injected pulp sheet. In a particularly preferred embodiment, the basis weight of the pulp sheet is about 180 to about 260 pounds / 3000 feet ² . The pulp sheet is then dried, evaporated as described above and heated to the point where there is no further loss of weight to carry out the reaction of the cellulose fibers with the carboxyl alkenes.

In an alternative embodiment, the cellulose fiber and the fluid mixture containing the carboxyl alkenes are contacted by forming a slurry of cellulose fibers in the fluid mixture (eg, by immersion and mixing). Thus, the fibers and alkenes may be contacted by including alkenes in the paper furnish of the wet laminated papermaking process known in the art.

A fluid mixture containing carboxyl alkenes is prepared and reacted by contacting with cellulose fibers to bring the degree of substitution on the cellulose molecule to about 0.25 to about 1.5, more preferably about 0.5 to about 1.0, most preferably about 1.0 (i.e. When calculated based on the moles of cellulose anhydrous glucose, from about 0.25 mole percent to about 1.5 mole percent, preferably from about 0.5 mole percent to about 1.0 mole percent, most preferably about 1.0 mole percent of cellulose hydroxyl groups are the carboxyl groups of the alkenes. Reacting to form a covalent bond).

The treated fibers are heated to a temperature and for a time sufficient to substantially remove the liquid medium and to allow the cellulose hydroxyl groups and carboxyl functional groups of the alkene to form covalent bonds. When the preferred carboxyl compound, polycarboxyl compound is used, the treated fibers substantially remove the liquid medium from the fiber, form anhydrides of the polycarboxyl compound and form covalent bonds between the carboxyl alkenes and cellulose hydroxy groups. Heated for a sufficient temperature and time. When water is used as the liquid medium, the treated fibers are preferably heated to at least about 100 ° C. to evaporate water. Evaporation and reaction typically occur when the treated fibers are heated at about 120 ° C. to 180 ° C. for about 30 minutes to 2 hours.

In a preferred embodiment, covalent bond formation is promoted with a suitable catalyst. Catalysts tend to speed up the reaction, reduce the degradation of cellulose fibers, and increase the yield of intermediate cellulose fibers. Any catalyst known in the esterification art may be used. Preferred catalyst is sodium hypophosphite (NaH ₂ PO ₂ ), which tends to increase yields and reduce degradation of cellulose fibers at higher reaction temperatures. The use of sodium hyperphosphite as an esterification catalyst is described, for example, in US Pat. No. 4,820,307 to CMWelch, which is incorporated herein by reference. The catalyst is suitably included in a fluid mixture containing carboxyl alkenes.

When the preferred 1,2-disubstituted alkenes are used, the resulting intermediate cellulose fibers with a degree of substitution of 1.0 have the structure as follows:

Where

R 'is OH or NH ₂

n is the degree of polymerization of the cellulose fibers (ie DP), which is at least 1, preferably 1 to 10,000.

The resulting intermediate cellulose fiber is then oxidized to form the modified cellulose fiber of the present invention. Prior to oxidation, the intermediate cellulose fibers are typically washed to remove any residual carboxyl compounds that do not react. The fibers may also be appropriately washed with a dilute aqueous solution of a base such as an aqueous sodium carbonate solution.

The oxidation process is carried out by contacting the oxidizing agent with the intermediate cellulose fiber under conditions which form an aldehyde group in the presence of carboxyl alkenes. The oxidation process is preferably carried out by forming a mixture of intermediate cellulose fibers and a suitable liquid medium, for example a slurry or other dispersion, and adding the oxidizing agent to the mixture under conditions in which aldehyde groups are formed in the presence of carboxyl alkenes.

Suitable liquid media are media that may assist in dispersing the fibers without severely disturbing the oxidation reaction. Examples of liquid media include water, organic solvents such as acetic acid, lower alcohols, chlorinated hydrocarbons, and mixtures thereof. Water is the preferred liquid medium. The amount of liquid medium and fibers in the mixture may vary over a wide range. Typically, the mixture comprises about 0.1 to about 50 weight percent fiber and 99.9 to about 50 weight percent liquid medium. Thus, the mixture may have a low consistency (e.g., about 1 to 3.5% by weight of fiber, 99 to 96.5% by weight of liquid medium), medium consistency (e.g., about 8 to 16% by weight of fiber, aqueous The liquid medium may be from 92 to 84% by weight. The consistency may be high (eg about 20 to 50% by weight fibers and 50 to 80% by weight of the aqueous liquid medium).

Suitable oxidizing agents include ozone and potassium permanganese. Ozone is the preferred oxidant. Ozone is the preferred oxidant in terms of efficiency, simplicity, economy, environmental impact and safety of the reaction.

Oxidation with ozone is carried out by introducing ozone into the mixture, for example by injecting gas into the mixture under pressure. The flow rate and pressure of ozone may vary over a wide range, but examples of conditions include flow rates of about 8.0 liters / minute and flow pressures of about 8 psig. In order to maximize the stability of ozone in the mixture, the mixture is preferably cooled as low as possible within the range in which the mixture is not frozen. The oxidation reaction is typically complete by introducing ozone under the conditions described above typically for about 30 to about 60 minutes.

During the oxidation step, aldehyde groups are formed on the carboxyl alkene residual phase of the intermediate cellulose fibers. While not wishing to be bound by theory, it is believed that at least some aldehydes are present on the fiber surface to facilitate bonding between the fibers during the papermaking process. Aldehyde groups may be formed within the fibers and / or at the fiber walls (ie, aldehyde groups in the fibers). Formation and quantification of aldehyde groups can be determined by known analytical techniques such as infrared analysis. Optionally, the presence of aldehyde groups is found to increase the wet strength of the paper product formed from the modified fibers compared to the corresponding paper product formed from the unmodified fibers. In general, for a given set of fiber weight, concentration of oxidant, and reaction conditions, the longer the exposure time to the oxidant, the greater the oxidation. Thus, the degree of oxidation can be easily optimized for a given fiber weight by quantifying the aldehyde content as a function of time by any of the methods described above. It would be desirable to avoid excessively oxidizing the fibers to excessively form carboxylic acid groups, which can be detected and quantified by the same technique.

Modified fibers also contain hydroxyl groups. While not wishing to be bound by theory, it is believed that the hydroxyl groups react with the aldehyde groups to impart wet strength to the paper product as further described herein.

When using the preferred 1,2-disubstituted alkenes, the resulting modified fibers having a degree of substitution of 1.0 have the structure as follows:

Wherein R 'and n are as defined above.

The resulting modified cellulose fibers of the present invention can be recovered by removing a large amount of liquid medium and then drying the fibers. For example, the modified fibers may be optionally further diluted, then sheeted using conventional wet laminated papermaking processes and then dried. Drying may be promoted by heating to a temperature sufficient to substantially remove the liquid medium (eg, by heating to about 85 ° C. to about 125 ° C.) to obtain a substantially constant weight. Thus, the modified cellulose fibers are collected for later use in the papermaking process. Optionally, a mixture containing modified cellulose fibers may be introduced into the continuous papermaking process without recovering the fibers as is known in the art (eg, paper furnishing of the wet laminated papermaking process).

Modified cellulose fibers of the present invention are useful in a wide range of papers and paper products. As used herein, the terms "paper" and "paper product" include objects and shaped articles such as sheets containing the modified cellulose fibers of the present invention.

In addition to the modified cellulose fibers described herein, the paper products of the present invention may include conventional or other papermaking materials. For example, the paper product may include conventional paper fibers, such as chemically modified fibers or unmodified cellulose fibers. The paper product may also contain a non-cellulose fiber polymeric material characterized by having a hydroxy group attached to the polymer backbone, such as glass fibers and synthetic fibers with hydroxy groups. Other fibrous materials, such as synthetic fibers (e.g. rayon, polyethylene and polypropylene fibers), may be used in admixture with natural cellulose fibers or other fibers containing hydroxy groups. Fiber materials having hydroxy groups may be chemically modified to incorporate aldehydes in the manner of the cellulose fibers of the present invention and incorporated into paper products. Mixtures of any of the foregoing fibers may be used in admixture with the modified cellulose fibers of the present invention.

Conventional papermaking additives known in the art include, for example, dry strength and wet strength additives, preservatives and paper softeners. As will be appreciated by those skilled in the art, the wet strength resin may be selected to impart either temporary or permanent wet strength. For example, polyacrylamides tend to further impart permanent wet strength to paper products formed from the modified cellulose fibers of the present invention.

Paper products are typically formed by wet laminated papermaking processes. Wet laminated paper making processes typically include providing a slurry containing papermaking fibers (optionally the slurry is referred to herein as paper furnish), on substrates such as porous forming wires (eg, Fourdrinier wires). Depositing a slurry of fibers, and curing the fibers into a sheet form under conditions in which the fibers do not substantially aggregate. Curing the fibers in the form of sheets can be performed by draining the fluid, for example by compressing the fibers against the porous wire (dewatering) with a screened roll (e.g., a cylindrical Dandy roll). It may be. Once cured, the fibrous sheet is then dried and optionally compressed if desired.

The drying step removes water and any other liquids to improve the wet strength of the paper product. The paper product may be dried by applying it to a high temperature (eg, 85 ° C. to 125 ° C.) for a time sufficient to dry, typically enough to retain less than about 10 water and / or liquid. Typical drying conditions are from 20 ° C to about 100 ° C. Without wishing to be bound by theory, as soon as the paper article comprising the modified cellulose fibers of the present invention is dried, the aldehyde groups of the modified cellulose fibers form adjacent cellulose hydroxy groups and hemi-acetals and / or N-acylhemiamials. do. These hemi-acetal groups are readily degraded by water, but serve to impart dry strength and initial wet strength to the paper product. Thus, when the paper product is exposed to an aqueous fluid, hemi-acetal and / or N-acyl hemiaminal groups return to the aldehyde group to provide temporary wet strength to the paper product.

The invention is particularly suitable for paper products to be treated with sewage systems, such as toilet paper. However, it will be appreciated that the present invention is not limited to disposable absorbent paper products (such as kitchen, body or other cleaning applications) and to absorption of body fluids (such as urine and menstrual blood) and can be applied to many paper products. Thus, examples of paper products include tissue paper and facial tissues, paper towels, basal absorbent materials, feminine physiological products (eg sanitary napkins, pantliners and tampons), adult incontinence products, and the like; And writing paper.

For tissue paper, the modified cellulose fibers of the present invention can be used in making tissue paper of any type. For example, the tissue paper of the present invention may be a uniform or multi-layered structure, and the tissue paper produced therefrom may be a single or multi-layered structure. The tissue paper preferably has a basis weight of about 10 g / m 2 to about 65 g / m 2 and a density of about 0.6 g / cm 3 or less. More preferably, the basis weight is less than about 40 g / m 2 and the density is about 0.3 g / cm 3 or less. Most preferably. The density will be from about 0.04 g / cm 3 to about 0.2 g / cm 3. The density of the tissue paper in paragraph 13, lines 61 to 67 of US Pat. No. 5,059,282, issued to Ampulski et al. On October 22, 1991. The method of measurement is described. (Unless otherwise noted, all amounts and weights for paper are based on dry weight) Tissue paper may be conventionally compressed tissue paper, pattern dense tissue paper, and uncompressed non-dense patterned tissue paper. Tissue papers of this type and methods of making such papers are known in the art, for example to Dean V. Phan and Paul D. Trokan, which are incorporated herein by reference August 2, 1994 Described in US Pat. No. 5,334,286, issued.

Test method

Strength test

Prior to the tensile test, paper products were aged for at least 24 hours in a conditioned laboratory with a temperature of 73 ° F. ± 4 ° F. (about 28 ° C. ± 2.2 ° C.) and a relative humidity of 50% ± 10%.

1. Total dry tensile strength ("TDT")

The test was performed at 73 ° F. ± 4 ° F. (approx. 28 ° C. ± 2.2 ° C.) and 1 sheet of paper (handsheet and other paper sheets as described above) in a conditioned laboratory with a relative humidity of 50% ± 10%. It is performed in inch by 5 inch (about 2.5 cm by 12.7 cm) pieces. Using an electrical tensile tester (Model 1122 from Instron Corp., Canton, Massachusetts), a crossover speed of 2.0 inches / minute (about 1.3 cm / minute) and 4.0 inches (about 10.2 cm) It was performed at the gauge length. When referring to the machine direction, it means that the sample is prepared so that the 5-inch side of the sample to be tested corresponds to this direction. For the TDT in the machine direction (MD), the pieces were cut so that a 5 inch sized plane was parallel to the machine direction of the paper product maker. For the TDT in the cross machine direction (CD), the pieces were cut so that the 5 inch sized plane was parallel to the cross machine direction of the paper product maker. Machine-direction and cross-machine direction of the machine is a term well known in the papermaking field.

MD and CD tensile strengths are determined by the calculations of the aforementioned techniques and conventional methods. The reported value is the mathematical mean of at least 8 pieces tested for the strength in each direction. TDT is the mathematical sum of the MD and CD tensile strengths.

2. Wet tensile strength

With the same size pieces as in the TDT, a crosshead speed of 0.5 inches / minute (about 1.3 cm / minute) and 4.0 inches (about 10.2 cm) using an electrical tensile tester (Instron Corporation, Model 1122) Was operated at a gauge length of. The pieces were moistened with distilled water at about 20 ° C. for a predetermined immersion time and then the tensile strength was measured. As in the case of the TDT, when referring to the machine direction, it means that the sample is prepared such that the 5-inch side of the sample to be tested corresponds to this direction.

MD and CD wet tensile strengths were measured by the calculation of the instrument described above and conventional methods. The reported value is the mathematical mean of at least 8 pieces tested for the strength in each direction. The total wet tensile strength for a given dipping time is the mathematical sum of MD and CD during the dipping time. Total initial wet tensile strength (“ITWT”) was measured by saturating the paper for about 5 ± 0.5 seconds.

The following non-limiting examples are provided to illustrate the present invention. The scope of the invention is determined by the following claims.

Preparation of Paper Web of Cellulose Fibers of Cis-1,2,3,6-Tetracyclophthalic Acid, Ozone Oxidized

Example 1 (handsheet)

Handsheets are prepared according to TAPPI Standard Method T205 essentially with the following modifications:

(1) using tap water adjusted to 4.0-4.5 to the desired pH with H ₂ SO ₄ and / or NaOH;

(2) forming a sheet on the polyester wire and dewatering with suction instead of pressurization;

(3) moving the initial web to a polyester papermaking fabric by vacuum;

(4) The sheet is then dried with steam in a rotary drum dryer.

To a 12 inch by 12 inch dry handsheet (base weight 28 pounds / 3000 feet ² ) of unmodified papermaking fibers, until 10% acid (fiber weight) and hyperphosphite 0.5% (fiber weight) were applied, An aqueous solution of cis-1,2,3,6-tetrahydrophthalic acid and sodium hyperphosphite (29 g / L) (pH 4) was sprayed. The handsheet was dried to constant weight at room temperature in a pressurized air oven. The sheet was then cured in a pressurized air oven at 180 ° C. for 30 minutes. The cured sheet was washed with demineralized water at pH 2 and dehydrated until 40% consistency. The resulting fibers of 40% consistency were fluffed and ozonated with a Welsbach Ozone Generator Model T-816 for 30 minutes to 1 hour at room temperature. The fibers were ozone oxidized below 0 ° C. with an oxygen flow rate of about 8.0 liters / minute and a flow pressure of reverse 8 psig.

Handsheets having a basis weight of 18 pounds / 3000 feet ² , made from the resulting fibers, have tensile strength as shown in Table I below.

Oxidation time (minutes) Total dry tensile strength (g / inch) Total Initial Wet Tensile Strength (g / inch) 30 593 117 60 1389 213

As shown in Table I, one hour of oxidation provides higher initial wet tensile strength than one that oxidizes for 30 minutes.

Example 2 (paper machine)

Pulp sheets with a basis weight of 260 pounds / 3000 feet ² (unrefined NSK fibers, for example, fibers with a DP of 1500) were formed on a conventional paper machine (Sandy Hill Manufacture) and 49% Wet compaction into a solid. A 20% solid aqueous solution of tetrahydrophthalic acid (THPA) and sodium hypophosphite at 60 ° C. was applied on the sheet to apply 10% (fiber weight) of THPA and 0.5% (fiber weight) of sodium hyperphosphite. The sheet is then passed through a can dryer portion at 300 ° F. for 2-3 minutes to dry the sheet and react the fiber with THPA to form esterified fibers. The resulting esterified pulp sheet was treated with ozone sequentially for 1 hour as in Example 1. The resulting fibers are handheld in conventional methods and instruments. The paper sheet has a basis weight of 18 pounds / 3000 feet ² , a calipers of 7.4 mils, a density of 0.142 g / cc, a total dry tensile strength of 2106 g / inch, and a total initial wet tensile strength of 586 g. / Inch.

A pulp sheet of weakly purified NSK with a basis weight of 260 pounds / 3000 feet ² (639 mL of Canadian standard degrees of freedom; for example, DP of 1500) was prepared and treated as described in the preceding paragraph. The resulting treated pulp sheet was ozonated and the resulting fibers were hand seated as described in the previous paragraph. The paper sheet has a basis weight of 18 pounds / 3000 feet ² , a caliper of 8.4 mils, a density of 0.125 g / cc, a total dry tensile strength of 2565 g / inch, and a total initial wet tensile strength of 794 g / inch. .

Comparable handsheets formed from Aspen or SF Ponderosa fibers treated as described in this example had slightly lower total dry tensile strength and total initial tensile strength than those obtained from sheets formed from NSK fibers. little.

While specific embodiments of the invention have been described and described, those skilled in the art will clearly appreciate that various other changes and modifications are possible without departing from the spirit and scope of the invention. Accordingly, it is intended that all such changes and modifications be included within the scope of the appended claims within the scope of the invention.

Claims (8)

1,2-disubstituted carboxyl having (i) cellulose fibers having a hydroxy group and (ii) a carboxyl functional group capable of reacting with the hydroxy group (i), wherein the double bonded carbons each form a single bond with another adjacent carbon atom Prepared by oxidizing a reaction product with a system-alkene, Wherein at least a portion of the hydroxy groups in the reaction product react with the carboxyl groups of the alkene to form a covalent bond, and wherein the reaction product is oxidized to form an aldehyde group. The method of claim 1, An aldehyde-modified cellulose fiber in which the carboxyl functional group of the 1,2-disubstituted carboxyl alkene is selected from the group consisting of carboxylic acid groups, acid amide groups and mixtures thereof and can form anhydrides. The method of claim 2, An aldehyde-modified cellulose fiber wherein said carboxyl functional group is a carboxylic acid group. The method of claim 3, wherein An aldehyde-modified cellulose fiber selected from said 1,2-disubstituted carboxyl cis-1,2,3,6-tetrahydrophthalic acid, cis-1,2,3,6-tetrahydrophthalamic acid and mixtures thereof. The method of claim 1, An aldehyde-modified cellulose fiber in which 0.25 to 1.5 mole percent of the hydroxy groups of the cellulose fibers react with the carboxyl functional groups of the alkene, calculated on the basis of moles of cellulose anhydrous glucose. A paper product comprising the aldehyde-modified cellulose fiber of any one of claims 1 to 5. A process for the preparation of aldehyde-modified cellulose fibers, characterized by comprising the following steps (a) to (d): providing a fluid mixture of (i) cellulose fibers having hydroxy groups and (ii) 1,2-disubstituted carboxyl alkenes having a carboxyl functional group capable of reacting with cellulose hydroxyl groups and a liquid medium; (b) contacting cellulose fibers with the fluid mixture to form treated fibers; (c) reacting a portion of the hydroxy groups of the cellulose fibers with the carboxyl functional groups of the alkene to form a covalent bond to form intermediate cellulose fibers; And (d) reacting the intermediate cellulose fiber with an oxidizing agent to form an aldehyde group. The method of claim 7, wherein wherein (b) and (c) comprise the following steps (i) to (v): (i) providing a slurry containing cellulose fiber and water; (ii) depositing the slurry on the porous substrate; (iii) curing the fibers into a sheet form under conditions in which the fibers are not substantially agglomerated to form a pulp sheet having a consistency of 20 to 50% and a basis weight of 180 to 260 pounds / 3000 feet ² ; (iv) contacting the cellulose fiber of the pulp sheet with a fluid mixture; And (v) reacting a portion of the hydroxy groups of the cellulose fibers of the pulp sheet with the carboxyl functional groups of the alkene to form covalent bonds to form intermediate cellulose fibers.